Multiple emulsion systems (broadly defined as systems in which water/oil and oil/water emulsion co-exist) are very valuable because these permit incorporation and enhanced delivery of benefit agents. Thus, these multiple emulsions have been used for many years, for example, in cosmetic and pharmaceutical areas to deliver cosmetic or pharmacological benefit agents (see for Example, U.S. Pat. No. 5,306,498 to Vesperini; or U.S. Pat. No. 5,567,426 to Nadaud et al.).
In general, however, as the level of cleansing surfactant (e.g., having high HLB, e.g., HLB greater than 10, preferably greater than 12) in such multiple emulsion systems is increased, the emulsions become less and less stable. Thus, for example, the level of cleansing surfactant in almost all the cosmetic and pharmaceutical art referred to above is below 5% by wt. of the compositions.
In U.S. Pat. No. 5,656,280 to Herb et al., and U.S. Pat. No. 5,589,177 to Herb et al. as well as in equivalent EP 717,978 and EP 715,842, both assigned to Helene Curtis, there is disclosed the stabilization of multiple emulsions in compositions containing high levels of conditioning surfactant. In these references, however, the stable multiple emulsion composition comprises surfactants (i.e., the conditioning surfactants of that invention) which must form stabilizing liquid crystals, i.e., lamellar liquid crystals. Those compositions described in the Herb patent where the surfactants formed an isotropic phase (for example, Example 29 at column 29 of U.S. Pat. No. 5,589,177 at lines 30-44) were unstable (see column 34, where stability of Example 29 is only 5 minutes). By contrast, the surfactant phase of the present invention is an isotropic surfactant phase, yet the multiple emulsion does not break into a simple emulsion when evaluated at room temperature for at least 2 weeks, preferably greater than 4 weeks, more preferably greater than 8 weeks, when measured at a temperature of about 25.degree. C.
Compositions comprising isotropic surfactant phases are advantageous over compositions comprising lamellar liquid crystal phase at least because (1) they can be formed using a much wider range of surfactant; and (2) they provide improved foam/lather.
Accordingly, it is an object of the invention to provide a surfactant phase which is not constrained in that it has to be lamellar phase.
It is another object of the invention to provide a surfactant phase (which is an isotropic phase) which contains high levels of surfactant and yet does not destabilize the multiple emulsion.